1. Field
The present application relates to a method and apparatus for determining optimal 3D reconstruction of an object of interest, particularly from angiographic projections.
2. State of the Art
Angiography is a commonly used imaging modality within a numerous variety of interventions. During such interventions it is very important that the clinician gets a good understanding of the object in question. For example in vascular interventions it is important that the clinician has all information concerning the part of the vessel tree of interest. This is necessary when, for instance, a stent is to be placed in a bifurcated vessel, where a bifurcated vessel is a main artery or vein that has split up into two or more further arteries or veins.
Two-dimensional (2D) angiographic imaging, such as X-ray, frequently lacks the possibility to visualize the bifurcation region correctly. Specifically, the carina position of the bifurcation, which is defined as the point where the vessel splits, is a challenge to visualize correctly with 2D angiographic imaging because of overlap of one or more of the vessel segments connected to the bifurcation.
If not all information about this bifurcated tubular shaped object is known by the physician, this can have severe consequences. For instance, an obstruction at the bifurcation can be missed or underestimated or the wrong stent dimension can be selected. This can lead to serious complications for the patient. Furthermore, in addition to the one-stent approach, new bifurcation stenting techniques, such as two-stent approaches and even use of dedicated bifurcation stents, are more and more used during cardiovascular interventional treatment of bifurcated vessels. These new treatment techniques require accurate information of the tubular shaped object in question. A way to acquire such information of the object under examination is through high resolution volumetric images acquired with CT or MR systems. These imaging acquisition systems need to have the patients, especially the part to be imaged, inside the apparatus and access for interventional treatment is cumbersome. Also these apparatus provide a great amount of image data, whose processing is time-consuming and makes it unrealistic to perform imaging sessions in real-time where the object of interest needs to be visualized in real time during the intervention.
In practice interventional treatment is generally performed under guidance of 2D images acquired with angiographic X-ray systems of the so-called C-arm or L-arm type. These systems allow acquisition of 2D images from different directions, also called 2D projections, of the object under examination. These different projections can be obtained by rotating the arm holding the X-ray source and the image intensifier around the patient.
A three-dimensional (3D) reconstruction from 2D images acquired in two different projections is possible however there remains some uncertainty also in the 3D reconstruction on the exact shape of the vessel around the bifurcation due to overlap in the 2D images used to reconstruct the bifurcated vessel in 3D space.
An example of the problems with overlap is visualized in FIG. 1. Only the last image shows the true shape of the bifurcation resulting in a proper visualization of the carina.
Of course one could try to find an optimal projection with trial and error, but the extended number of images obtained during the intervention increase the radiation dose, the amount of contrast fluids, and can significantly increase the procedure time, all of which may have a negative influence on the health of the patient.
Document EP1280459 discloses a method for helping the clinician to reduce the number of perspectives needed for a proper 3D reconstruction by using a 3D model for determining two 2D projections upon which a new 3D model is to be reconstructed in order to better represent the object of interest. This document, although going in the right direction, is, however, aimed at straight arterial segments and requires further exposure of the patient to obtain at least two new projections.
There's thus the need for a method to assist the clinician to analyze the details of the bifurcation with the number of images needed reduced to an absolute minimum while also obtaining the maximum amount of image information concerning the bifurcated tubular shaped object under study.